"I didn't know it was illegal," said a van driver as he sat in a traffic jam, his mobile phone glued to his ear.

He carried on chatting regardless.

The driver of the car behind was also in the dark about the phone laws.

"What am I supposed to do?" he said.

"The phone rang and I answered it. I need to take calls for work."

These drivers were lucky. It was a reporter from The Argus who knocked on their car window, not a police officer.

From yesterday, anyone behind the wheel of a vehicle with the engine running is liable for a £30 fixed penalty fine if they use their mobile, even if they are in a queue or waiting at lights.

The cost can rise to £1,000 if the matter goes to court and to £2,500 for drivers of vans, lorries, buses and coaches.

Drive carelessly or dangerously when using a phone and the penalties include disqualification, a large fine and up to two years in prison.

Ministers also plan to increase the penalty by making it subject to three points and a £60 fixed penalty, although this will need to go through Parliament if it is to reach the statute books.

The only exemption to the rule is making a 999 or 112 emergency call.

Hours after it came into effect, a woman in Dundee became the first person in Britain to be fined.

Police in Sussex have adopted a softly-softly approach, preferring to educate drivers rather than punish them, for the first two months at least.

Which is probably just as well.

For our investigation, we headed to the temporary car park near Preston Park, otherwise known as the A23 into Brighton, where roadworks have led to jams round the clock.

Where better to find frustrated motorists making a quick call to say they will be running a few minutes late?

Within minutes, the first offender was caught on camera.

The man, a plumber in a white van, said he had heard about the changes but did not realise they had come into force.

He said: "There needs to be more notices around. Unless you sit in front of the TV all day, how are you supposed to know about it?"

The man, who asked not to be named, did not realise the law extended to drivers stuck in congestion.

He said he usually took work calls while driving but would invest in a hands-free kit to avoid fines after being snapped by The Argus.

Another van driver caught chatting on his mobile said he had a hands-free kit but had left it at home. He was aware of the £30 fine but again did not realise the rules extended to stationary vehicles.

He said: "I suppose it makes sense to stop people driving while making calls. But it will take some getting used to. I'm on the phone all the time, especially when I'm stuck in traffic."

Most of the people we caught were white van drivers making work calls.

Some car and van drivers admitted to crossing their fingers and ignoring the law.

In a national survey, more than a third of drivers admitted they planned to use their mobiles while at the wheel.

Just 17 per cent claimed they would switch off their phone while on the road. This is despite research showing people are four times more likely to have a crash when using a mobile.

Other law-abiding drivers were pleased the law had come into place.

Philip Harding, a 26-year-old student at Brighton University, said: "I stopped using my phone in the car a while ago as I think it is too distracting. I might consider getting a hands-free kit in the future but for now I'm happy not to use my mobile while driving."

Chief Inspector Ian Jeffrey said police did not plan to make any spot checks on drivers in Sussex.

He said: "Our approach at the moment is very much about education. We are trying to raise awareness in drivers and to generate compliance.

"If we are out on patrol and see someone using a hand-held phone, we will stop them and bring the legislation to their attention.

"But we are carrying on with business as usual. At the end of the day we are there to respond to crime incidents."

But he warned drivers not to be complacent.

He said: "Officers can use their discretion with the enforcement policy. If there is a bad crash, it could be brought in as an aggravating factor.

"It is all about road safety and reducing casualties. I think we've all followed a motorist who was swerving or going too slowly and wondered what was wrong.

"When you get past them you realise they have a mobile phone to their ear. You can see they are distracted and driving badly."

It is not just making or receiving a call which can land motorists in hot water. Sending or receiving text messages is illegal if you need to hold your handset.

Employers may also be liable if they fail to forbid employees to use phones on company business.

The only way to avoid a fine is to use a hands-free car kit with the phone in a cradle on the dashboard.

The kits costs about £150, including installation.

Alternatively, drivers are advised to let the phone ring and pull over to a safe place before calling back.

For more information, visit www.thinkroadsafety.gov.uk